There are many applications where it is necessary to spray a fluid material onto a target surface, often the ground. This application is notable for example in agriculture, horticulture and such things as golf course maintenance and pest control where chemicals are mixed with water and then sprayed on the ground, on plants growing from the ground, on bodies of water, and the like. Various fluids must also often be sprayed for example on roadways and in industrial applications to apply coatings and treatments to products passing by on a conveyor or the like.
Spraying is accomplished with sprayers, either self-propelled or towed units, and with aerial sprayers mounted on airplanes or helicopters. Such sprayers commonly comprise a tank of fluid, a pump for pressurizing and distributing the fluid to spray nozzles and means to control the fluid pressure. Sprayers typically have a plurality of nozzle bodies, each securing a spray nozzle tip, mounted on booms which swing in for transport and out for operation. Airplane mounted sprayers typically have a boom fixed to the wings.
The nozzle locations are spaced apart on a boom, perpendicular to the direction of travel, at a standard spacing distance which corresponds to the spray pattern of the nozzle tips. The same size nozzle tip is in operating position at each nozzle location, providing a consistent application rate across the width of the sprayer. Typically the nozzle tips are mounted in a nozzle body extending downward from the boom which carries the liquid agricultural products from the boom to the nozzle tips located in the bottom of the nozzle body. The nozzle body typically comprises an upper end connected to the boom and a channel extending downward to the nozzle tip mounted in the bottom end. A mesh strainer is commonly placed in the channel of the nozzle body between the nozzle tip and the boom. A typical strainer is provided by a hollow cylinder with wire mesh walls. Such a strainer and nozzle body is disclosed in U.S. Pat. No. 8,936,207 to Swan.
A problem with applying agricultural products such as herbicides is that even moderate air movement from wind, thermal conditions, and the like, can move the chemicals from the field being sprayed onto adjacent fields and, especially where the adjacent crop is of a different type and susceptible to the chemicals being sprayed, cause serious damage. Where fields are adjacent to urban or like otherwise occupied areas health issues also arise. This “drift” of chemicals is significantly affected by the size of the droplets being sprayed, with larger droplets being less susceptible to drift than smaller droplets. Conversely, it is generally the case that smaller droplets provide a better plant coverage than larger droplets, with corresponding increased efficacy in achieving the products aim, such as killing undesirable plants and weeds in the case of a herbicide.
Government regulations in some jurisdictions require a “label” on agricultural chemical products that indicates the conditions under which the product may be used, including the required application details such as limited environmental conditions, nozzles, nozzle droplet size classifications (droplet sizes), no spray zones, buffer zones, and other application details.
United States Published Patent Application Number 2008/0087745 of Pearson et al. discloses an air induction nozzle assembly for reducing the number fine small droplets dispensed from a sprayer nozzle. The assembly draws ambient air into the liquid flow stream for stabilizing the liquid prior to discharge from the nozzle.
U.S. Pat. No. 3,934,823 to Reed discloses angled tangential pre-orifices to impart a swirl to the swirl chamber which sprays into a second swirl chamber where the liquid appears to mix with air drawn into the chamber through the center of the hollow cone spray pattern dispensed from the nozzle tip which pattern comprises droplets of an increased size.
It is also known to provide a pre-orifice in the nozzle body above the nozzle tip. The pre-orifice device defines a hole which has a smaller flow rate than the nozzle tip and so controls the rate of flow and reduces the pressure at the nozzle tip so that larger droplets are dispensed from the nozzle tip. Wilger Inc. of Lexington, Tenn. makes and sells such pre-orifice devices that fit into the channel of the nozzle body between the nozzle tip and the boom, in the same location as the mesh strainer.
Similar problems occur in industrial applications where small droplets can fog and move off target onto machinery and surrounding areas.